Wiring a 12V Auxiliary Battery in Enclosed Trailer to 7-way Connector and Breakaway Battery

Updated 10/06/2015 | Published 10/04/2015

Question:

I read your article on adding a 12v deep cycle battery to an enclosed trailer Adam R. I think I understand most of what you were telling Jay C about running the black 12v feed from 7pin to + on new deep cycle battery. But then you say run the ground of other battery to frame of trailer. This is where I was getting a little lost!!! Do you run black feeds off 7pin to BOTH batteries and ground BOTH too frame? Or do you run black 12v feed to new larger battery +, then run a wire from - over too the + of the smaller brake battery and then run that battery - too trailer frame? A drawing of this set up would be helpful for all those people like me trying too add a battery for a trailer interior light or a winch. I attached a similar drawing of what would be helpful, but its missing a few wires and the other battery we are talking about adding. Thanks in advance for your help.

asked by: Shayne G

Helpful Expert Reply:

You will want to run the 12V wire from the 7-way trailer connector to the positive terminal on the larger battery. Then you will want to connect the larger battery to the breakaway battery from positive terminal to positive terminal, using 10 gauge wiring, like # 10-1-1. The negative terminal from the breakaway batter will connect to the negative terminal of the larger battery. The larger battery will ground from the negative terminal to the trailer frame.

I have attached a diagram of the battery connections for you.

This set-up will allow the breakaway battery to maintain a charge from the auxiliary battery, and the auxiliary batter will pull a maintenance charge from the vehicle battery when the trailer and vehicle are connected.

expert reply by: Victoria B